Photoacoustic measurement of thermal diffusivity of polymer foils

The photoacoustic measurement of polymer foils, typically 170–200 μm thick, is discussed. It is shown that the measurement based upon the phase lag between the front and rear illuminations is applicable only in a limited range of frequencies from 6 to 12 Hz. The dominant mechanism responsible for the photoacoustic signal, in almost the entire frequency range 10–100 Hz, is proven to be the thermoelastic bending of the foil samples. The thermal diffusivity is then obtained from the frequency dependence of the front-phase illumination data.